1. Field of the Invention
The invention relates to a fin for heat exchangers with at least one louver arrangement in the region between associated tubes for the heat transfer from one medium to another medium. More specifically, the louver arrangement is provided with an inflow part, an outflow part corresponding to the inflow part, with both flow parts having one outside louver, at least one intermediate louver and one inside louver.
2. Related Technology
The majority of the heat exchangers currently used in automotive applications possess a heat transfer core which contains heat transfer tubes, arranged one above the other in series, and fins between the tubes, whereby louvers are located in the fin surface. Heat transfer is from the heat transfer tubes to the fins with louvers, or vice versa. The louvers direct medium stream over the fin surface and through the fin surface, create a controlled degree of turbulence and are intended to enhance the heat transfer between the flowing medium and the fin.
In conventional fins particularly, the intermediate louvers are provided with louver geometry elements “of equal louver length L”, “of equal louver angle of inclination α, and “of equal louver width B” in the inflow part and the corresponding outflow part each.
The louver geometry element “all louvers of equal length L” essentially means that the passage slots of all louvers, and thus all louvers, are of equal length.
The outside louver, the intermediate louvers and the inside louver of each flow part, if there is the louver geometry element “all louvers of equal louver angle of inclination α”, have an equally directed angle of inclination. However, the directions of the angle of inclination in both flow parts are different, but mirror symmetrical to the fin midplane. Further the intermediate louvers have, if they have the louver geometry element “of equal louver width B”, an equal width and differ from the widths of the bent parts of the outer louver and the inner louver, which in most cases are equal to the half of the width of the intermediate louvers.
Other lover fins for heat exchangers are described in U.S. Pat. No. 4,328,861, whereby the heat exchangers have a structure of heat exchanger tubes and a fin core or flat fin baffles. The heat transfer tubes are designed in from of flat tubes. The fins are equipped with Venetian blind-like louvers extending parallel to the row of tubes in longitudinal direction inclusive of associated passage slots and have a piece reaching beyond the row of tubes. The fins between the tubes have passage slots of constant length, outside of the tube region there is a row of slots progressively shortened in longitudinal direction. Each of the slots outside of the tube region is shorter the normal slots arranged in row between the adjacent flat tubes, whereby the row of slots shortened in longitudinal direction is formed near to the outer edge of the projecting piece of the fin beyond the edges of the flat tubes and the shortest slot is arranged adjacent to the edge of the row of flat tubes. Therefore, outside of the flat tube regions in the row of longitudinally shortened louvers, each louver is shorter than the length of the normal louvers located between the adjacent louvers in a row, whereby the row of longitudinally shortened louvers is arranged formed in the projecting region of the fin between the outer edge of the fin beyond the end of the row of tubes.
Another heat exchanger with enclosing louver fin channels is known from U.S. Pat. No. 4,958,681. In the heat exchanger there is a plurality of round tubes and a plurality of fins located between the tubes. The fins are surrounded with many louvers and are thermally connected to the tubes, in order to enhance the heat transfer capacity of the heat exchanger. The fins consist of louvers and flat regions. The louvers are located between the pairs of tubes and are arranged at a distance to them on an adjacent fin region and by means of circular arc-shaped flat regions of equal width, which serve as circular-arc circulation channels of equal width. The ratio between the width of the circular-arc circulation channels and the distance between the adjacent tubes is to have an optimal value, whereby the louvers are intended to create the effect that heat transfer and air pressure drop of the heat exchanger increase when the characteristic of the heat transfer increases against the air pressure drop.
A tube-shaped heat exchanger for air conditioning units is described in U.S. Pat. No. 5,117,902, which consists of a plurality of fin plates arranged at regular distances parallel to each other; a plurality of heat transfer tubes arranged in at least one row and vertical to the fin plates; a plurality of projecting strips on each fin plate, whereby the strips are vertical to the air stream and formed projecting from the fin plate surface, and at least one diverting surface on each fin plate, whereby the surface extends along the central line of the row of heat transfer tubes.
In such a tube heat exchanger, air can flow between the fin plates while a liquid can flow in the heat transfer tubes. Each projecting strip can incline in two directions, depending on the direction of flow. In addition, the number of projecting strips of the row near to the longitudinal edge of the fin plate is bigger than the number of strips in the row near to the central line of the heat transfer tubes. No strips are provided on the diverting surface.
In U.S. Pat. No. 5,669,438 a corrugated heat transfer fin with a series of flat fin walls is described. The fin walls are one-piece folded with alternating crest lines, with a given fin wall width measured between the crest lines. The crest lines are established such that they can be connected to parallel, flat heat transfer tubes to form fluid flow passages existing between neighboring or adjacent fin walls and the tubes. A fluid is pressed through the tubes in a direction generally parallel to the crest lines. Each of the adjacent flow passages has also a restricted section within the inner surface of a crest line and an opposite, non-restricted section between the outer surfaces of the two adjacent crest lines. Each fin wall is formed with a series of one-piece, essentially planar louvers are bent out of the wall, whereby each of the louvers has a length generally parallel to the fin wall width.
Each louver is inclined from and through the plane of its fin wall about a slanting axis. Hereby one diagonal half of the louver is essentially completely moved onto one side of the fin wall and, accordingly, the other diagonal half of the louver is essentially moved onto the other side of the fin wall. The diagonally opposite corners of the louvers are moved into the non-restricted sections and from the restricted sections of the adjacent flow passages relative to each of the fin walls.
U.S. Pat. No. 5,730,214 describes a cooling fin heat exchanger with adjustable louver arrangement in which the louvers have varying angles. The louver arrangement consists of three parts—an inflow part, a louver-free central part and an outflow part. The inlet part and the outflow part each have an outside bent louver and several intermediate louvers. All louvers are arranged in symmetry of the inflow part and the corresponding outflow part to the central part midplane. The central part is connected to both inside intermediate louvers opposite to each other and offset to the fin plate plane. The intermediate louvers with the louver geometry elements “of equal louver length L”, “of unequal louver inclination angles α increasing beginning from the outside bent louvers directed to the central part”, and “of equal louver width B of the intermediate louvers” with the louvers being formed over the entire louver width are provided. Symmetrical to the central part in the inlet and outflow parts, outside bent louvers with unequal louver inclination angles are also provided. While the louvers within each traditional set of patterns “inflow part/outflow part” are uniform in length, width, slope and direction of the angle of inclination, the amount of the angle of inclination in each case can increase from the outside louver to the inside louver. In this case, the angles of inclination increase in direction of the air flow in the inflow part directed to the central part and at the same time continuously decrease in the outflow part. The louver inclination angles α are given, particularly, increasing beginning from 22° related to the outside bent louvers over 30° up to 40° relative to the last inside intermediate louvers for the inflow part, and accordingly decreasing for the outflow part. Thus, the louver inclination angle essentially stepwisely increases in direction to the central part and again stepwisely decreases in the outflow part up to its last outside bent louver to the angle of the outside bent louver of the inflow part. This means that essentially there is louver symmetry of the inlet and outflow parts relative to the central part. While the bent parts of the outside bent louvers have a width of only approximately half the louver width, the louvers connected to the central part have the same louver width as the other intermediate louvers. The central part is offset parallel to the fin plate plane at a distance in relation to the other flow parts.
A problem consists also in that, due to the big angles in the region of the central part, there are small turbulences which make the air flow onto the louvers in the region of the outflow part.
Another heat exchanger with louvers, which generate air turbulences, in the fins and the device to manufacture the louvers as well as a process to manufacture the fins are presented in U.S. Pat. No. 5,738,169. The heat exchanger consists of at least one row of flattened tubes through which a heat carrier flows. A fin rich of turns is, between two adjacent tubes, connected to the tubes. Within the fin there are a plurality of louvers, with each louver forming a longitudinal slot opening. A fluid to be heated or cooled by the medium passes the slot openings. An edge corrugated over one or several louvers causes turbulences in the fluid. The turbulences disturb the laminar flow of the fluid along the associated louvers.
From U.S. Pat. No. 5,765,630 a radiator with air flow directing fins is known, the fins being arranged at a defined angle relative to the sectional area of the radiator core. Air flowing into the radiator is accordingly diverted by the fins such that they go together with the angle of incidence of the fan blades blowing air into the radiator.
All known fins with their louver arrangements pose the problem, among others, of not having the optimal structure that makes possible a maximum heat transfer from one to another medium and a low pressure drop of the flowing medium after having passed the fins.
Therefore it is the object of the invention to provide a fin for heat exchangers which is adapted to be suitable so that the medium flow existing at the fin is optimally passed through the louver slots, the medium flows onto the louvers largely contacting them, turbulences are created, and a maximum heat transfer, as well as a low pressure drop within the flowing medium, are achieved.